Expectations for runway incursion prevention and runway confirmation systems are becoming increasingly common for commercial aircraft. One method of providing runway incursion/prevention is to use an enhanced vision system (EVS) to assist a pilot in identifying runways or obstacles. EVS systems employ a sensor, such as a visible-light camera or an infrared sensor, to provide additional information in low-visibility runway approaches.
Recent efforts have revealed a desire by users of enhanced vision systems to have an alternate means to descend below alert height (i.e., 100 feet) when the camera or infrared sensor typically used in such a system is incapable of allowing the pilot to confirm the presence of the runway beneath the aircraft. In certain low-visibility situations, infrared sensors cannot provide assurances adequate to descend below alert height. One proposed alternate means is to use weather radar returns of the runway. Because weather radar is already installed on the aircraft, no additional sensor system would have to be installed on the aircraft. The X band of the electromagnetic spectrum is used by certain weather radar systems and may provide satisfactory radar returns in situations in which an EVS infrared sensor is ineffective.
For weather radar to be an effective alternative to EVS for runway incursion prevention and runway confirmation functions, the radar must identify the runway with high integrity and high availability, even when ground clutter is present. In urban environments, it may be difficult to distinguish the runway from freeways. In rural environments, depending on the condition of the runway and the surrounding terrain, radar return contrast between the runway and the surrounding terrain may be low. Designing a radar-based runway detection system which is capable of operating across all these environments may be difficult and expensive.
One way of improving the detection capability of the radar without adding excessive radar design complexity is to add more correlation points between the radar return and the expected runway. In known systems the stored data, to which the radar return is correlated, consists of runway ends and perhaps location of landing lights at the runway ends. Attempts have been made to correlate sensed radar data with stored visible light images, such as publicly available satellite images or aerial photographs of runways, to increase integrity of the radar runway confirmation. However, visible light images do not necessarily correlate well with weather radar returns, which are typically in the X band. What is needed is a runway recognition system that would provide a highly predictable correlation between a radar return of a runway and a stored image representing the runway.
It is therefore an object of the invention to provide a method of recognizing a particular runway in low visibility conditions.
It is another object of the invention to provide a runway recognition system using weather radar returns of a runway.
It is another object of the invention to provide a runway recognition that minimizes the additional hardware to be placed on an aircraft.
A feature of the invention is comparing weather radar returns of a runway with a previously obtained runway image having a similar spectrum range as the weather radar return.
Another feature of the invention is to provide a unique method of collecting X-band information, i.e., via radar itself on landing.
An advantage of the invention is that no additional hardware is required to be installed when a weather radar system is present on an aircraft.
Another advantage is that the weather radar uses a portion of the electromagnetic spectrum particularly useful in some types adverse weather, and particularly in types of weather that are problematic for other known sensor systems.